Rio Ribeira, known formally as the Rio Ribeira de Iguape, is a remarkable river flowing through the states of Paraná and São Paulo in southeastern Brazil, ultimately emptying into the Atlantic Ocean near Iguape. One of the most ecologically significant rivers in the region, it winds through a relatively sparsely populated landscape still graced by stretches of intact Atlantic Forest. Notably, no dams have been constructed on the river, preserving its natural flow regime and making it one of the few undammed river systems of its size in southeastern Brazil. This free-flowing character gives the river a distinctly wild quality, with natural hydrology shaping its pools, riffles, and channel structure throughout its course.